Loss of forest cover leads to population isolation in an imperiled, headwater-specialist fish

Anthropogenic land use degrades matrix, habitat, and corridors and can disrupt dispersal rates or dispersal attempts, resulting in population connectivity patterns that reflect the cost (or resistance to dispersal) imposed from degraded conditions (isolation by resistance; IBR) rather than that of geographic distance alone (isolation by distance; IBD). As a small-bodied, benthic riverine species with relatively low dispersal capability, the imperiled Kentucky Arrow Darter (KAD), Etheostoma spilotum, is vulnerable to the negative effects of anthropogenic land use on population connectivity. To inform conservation efforts for KAD, we identified the primary drivers of population isolation (IBD vs. IBR) in the species using a riverscape genetics framework. We created resistance surfaces from landscape variables that may influence KAD occurrence and dispersal success (elevation, presence of dams, stream order, and percent landcover type). Cumulative resistance was correlated with FST values using a linear mixed effects model in R package corMLPE. Though we found significant, positive relationships between genetic and geographic distances, analyses of single and multi-surface resistance models demonstrated that isolation by resistance was the primary driver of genetic distances among KAD populations. In particular, decreased forest cover was linked to high genetic differentiation. These results illustrate that population connectivity primarily degrades through resistance to dispersal rather than geographic distance between populations. Conservation efforts should focus on mitigating past and ongoing land use associated with deforestation, in addition to genetic rescue, as habitat restoration will not likely occur quick enough to prevent continued declines in KAD populations.